Due to their small size and fragile nature, integrated circuit semiconductor chips are commonly packaged in integrated circuit chip carriers. A chip carrier typically comprises a substrate of ceramic or other rigid insulating material having an integrated circuit chip mounted thereon and containing a plurality of conductors which extend from adjacent the chip to the periphery of the substrate where they are terminated by enlarged contact areas or contact pads.
Frequently, a multi-chip carrier substrate is incorporated within a frame or housing which protects and supports the multi-chip carrier substrate and the chips thereon, and provides a connector to electrically connect the substrate to a printed circuit board or other external circuitry. Generally, the frame or housing contains a plurality of leads. One end of each of the leads extends into the housing to be electrically connected to one of the contact pads on the substrate, and the opposite end of each of the leads extends out of the housing to be connected to contacts on the printed circuit board either directly or through a socket connector.
In the past, integrated circuit semiconductor chip carrier systems have been characterized by including rigid housing structures which included glass seals to seal between the housing and the leads extending therethrough to hermetically seal the housing. The housing structures provided in the prior art have been used as structural members which were not designed with any non-rigid characteristics. In other words, the housing was made of rigid plastic which not only supported the leads, but also provided the structure to support the substrate. Such systems have not been fully satisfactory due to difficulty in maintaining the hermetic seal as the chip carrier and substrate are exposed to various temperature. As result of variations in thermal expansion and contraction of the rigid housing components, the hermetic seal of the frame was lost. Another problem with the chip carriers of the prior art was due to very high cost of such structures. Prior semiconductor chip carrier systems have also included substrates of ceramic or other such non-flexible materials on which the semiconductor chips were mounted. The ceramic substrates were provided with conductors embedded within the substrates (multi-layer co-fired ceramic substrates), or built up layer by layer on a surface of the substrates (thin or thick-film ceramic substrates). In some instances, the conductors were incorporated into films deposited uniformly on a surface of the substrates. Electrical connection from the chip to the conductors of the substrate, and from the conductors of the substrate to the housing leads, was made by thin gold or aluminum bond wires to compensate for variations in thermal expansion and contraction and physical distortion of the various components of the system, and to provide connections between the semiconductor chips and the substrate. Such connections, however, are expensive to fabricate and have not proven to be entirely satisfactory.
Many prior semiconductor multichip carrier systems were also limited in size. In particular, prior processes for manufacturing ceramic substrates were generally unable to produce sufficiently flat substrates in sizes larger than about two inches by two inches due to the difficulties of maintaining dimensional stability of the ceramic during firing. The quality of the surface finish on prior ceramic substrates was also such that high-density, thin-film interconnects were not possible on the substrate.